In recent years, a demand for dialkylzinc has been growing as a catalyst or a reaction agent for polymerization or pharmaceuticals manufacturing, and as a substance for forming zinc oxide that forms a transparent conducting film used for an electrode of solar cells or semiconductor manufacturing devices. As one of the methods for manufacturing dialkylzinc, a reaction of zinc chloride and trialkylaluminium shown in an equation (1) has been known as described in Patent Documents 1 or 2.ZnCl2+2R3Al→R2Zn+2R2AlCl  (1)
Dialkylaluminum monohalides, such as dialkylaluminum monochloride obtained as a coproduct of dialkylzinc obtained in the above-mentioned reaction, have functions such as catalytic action for various polymerization reactions, and the usefulness thereof has been observed in various fields.
Dialkylzinc and dialkylaluminum monohalide are manufactured as follows. Usually, first, dialkylzinc which has a lower boiling point is obtained by distillation of a reaction liquid in which dialkylzinc and dialkylaluminum monohalide are produced by a reaction such as the equation (1), then next, dialkylaluminum monohalide which has a higher boiling point is obtained by distillation of the reaction liquid.
While a still pot residue after distillation of dialkylzinc mainly contains dialkylaluminum monohalide, a zinc component still remains. Accordingly, the zinc component is contained in dialkylaluminum monohalide obtained by distilling the pot residue. Various methods for reducing the concentration of zinc component contained in dialkylaluminum monochloride have been reported. For example, Patent Document 3 has disclosed a method for adding trialkylaluminum including alkylaluminum hydride to a pot residue after distilling dialkylzinc, and Patent Document 4 has disclosed a method for adding alkylaluminum sesquichloride to a pot residue after distillation separation of dialkylzinc. However, dialkylaluminum monochloride and trialkylaluminium which have the same number of carbons in alkyl groups have an approximated boiling point. Therefore, separation of these products by distillation is difficult.
Further, Patent Document 5 has reported a method for heating a pot residue at 150 to 240° C. in an inert gas atmosphere after distillation separation of diethylzinc. Patent Document 6 has reported a method for adding aluminum chloride and triethylaluminum, heating the mixture, and subsequently distilling dialkylaluminum monochloride. However, these methods increase steps, additionally, the zinc concentration in diethylaluminum monochloride obtained is 200 mass ppm, 100 mass ppm, or the like, and is not fully reduced.
As mentioned above, a method for manufacturing dialkylaluminum monohalide which substantially includes no zinc component, by which dialkylzinc is separated by distillation from a reaction product obtained by reaction of zinc chloride and trialkylaluminium, and then dialkylaluminum monohalide is separated by distillation from the reaction product at a high yield on an industrial scale, is still desired.